The present invention relates generally to irrigation systems and pertains particularly to method and apparatus for the controlled irrigation of individual plants.
Agricultural production is heavily dependent upon the application of adequate water to sustain plant growth. In many areas of the world, however, rainfall is insufficient in amount and uncertain as to intervals for successful agricultural production. In order to sustain agricultural production in these areas, water available from rivers, lakes or the like must be applied to the crops by various irrigation methods.
Numerous irrigation methods are known and many of these methods are satisfactory for most crops. The usual methods of irrigation available are gravity flow, sprinkler, and drip irrigation. Gravity flow for flood irrigation is adequate in areas where adequate water is available and the slope of the terrain is suitable. This is perhaps the easiest and less expensive method where suitable.
The sprinkler method of irrigation is suitable for areas where gravity feed is not feasible and permits greatly expanded use of agricultural land. The application by sprinklers is also suitable for many crops.
The drip method of irrigation has been developed for areas where water is not plentiful and provides a more efficient use of available water than the previous two mentioned methods.
One problem with each of these methods is that much of the water available for irrigation purposes includes or contains some salts. They become a problem for plants which are salt sensitive because salts tend to accumulate within the soil around the plants due to evaporation of the water from the soil surface and uptake of water by the plants.
Another problem, with at least the sprinkler system of irrigation, is that some plants are sensitive to the effects of salts deposited on leaf surfaces from sprinkler water evaporating from these surfaces. In addition, the free moisture on plant tissue is at times conducive to the development of pathogenic bacteria and fungi. Even with carefully placed sprinklers, wind can cause uneven application of the water by the sprinklers and also cause water to accumulate on the plants.
Another problem with sprinkler irrigation is that the power requirements are generally high.
The so called drip irrigation is a high-frequency pressure system that is a recent development permiting more efficient use of irrigation water. This system since its inception has become quite popular and is quite extensively used throughout the world. High frequency pressure systems generally permit a much higher level of efficiency of use of the water than either gravity or sprinkler systems. They also have a lower power requirement than sprinkler systems and can be designed to operate with a low per acre labor input.
This concept of high-frequency irrigation involves the addition of water to the crop at frequent intervals, at times daily, in controlled amounts approximately equal to that used by the crop in evapo-transpiration plus an additional amount to effect some leaching of the soil to prevent accumulation of salt to a level adverse to the crop.
Several methods have been used in the high-frequency application of irrigation water to agricultural crops. These methods include the dripper which is an emitter that discharges water in discrete drops at a rate of from one to three gallons per hour, the porous hose which may ooze water at a rate of from 1/10 to 1 gallon per hour per foot of hose, a spitter which is commonly a fixed angle sprayer which discharges water at a rate of from 1/10 to 4/10 gallons a minute as a fan spray, and the bubbler which is an open port that emits water at a low discharge velocity at a volume from one to three gallons per minute. Each of these methods has advantages and disadvantages.
One of the hazards of irrigated agriculture is the result of buildup in the soil of salts remaining after the evapo-transpiration of water by the crop. Many irrigation waters, for example, contain upward of 11/2 tons of salts per acre foot of water and with crop usage of water in hot climates reaching from four to six acre feet per acre annually upwards of eight tons of salt may be deposited in the soil per acre per year. Such a high concentration of salt can have an adverse affect upon the crops grown in the area.
One approach to the prevention of buildup of deleterious levels of salt within the crop root zone is by adding somewhat more water than required by the crop and leaching the accumulating salts downward below the root zone. The degree of leaching is a function of the volume of water applied in relation to the volume of soil and the evapotranspiration requirements of the crop.
Salt accumulation near the soil surfaces is particularly a problem in arid regions where there is insufficient rainfall to leach the salt to a depth below the root zone. It is, therefore, desirable to prevent an appreciable accumulation of salt near the soil surface above the root zones of the crops. The dripper and porous tubing approach to high frequency irrigation systems frequently results in an undesirable accumulation of salt near the surface of the soil. Good application of the spitter concept, however, permits a relatively large surface area to be wetted with resultant downward movement of salt and can result in a minimum of salt accumulation in soil over the root zone as compared with porous tubing or drippers. The use of the spitter method, however, has not been satisfactory because of the lack of satisfactory equipment available to permit its efficient use for many crops.
Citrus and other such crops, for example, even those sensitive to salt and other such problems associated with irrigation are adaptable to arid regions where proper irrigation methods and apparatus are available.
Irrigation equipment and methods for use in orchards must meet several fairly exacting requirements, such as equipment should be out of the way of cultural and harvesting operations as well as sufficiently strong to withstand any chance contact which might result from harvesting and cultivating equipment. The equipment method should also be capable of wetting the same area each time that water is applied and should be readily accessible for checking and maintaining for satisfactory performance. The equipment must also be sufficiently rugged to withstand adverse elements of the weather.
The prior art approach to various irrigation methods and equipment is exemplified by the following U.S. reference patents: No. 2,747,935 issued May 29, 1956 to Szanthay; No. 2,807,507 issued Sept. 24, 1957 to Cook; No. 3,301,515 issued Jan. 31, 1967 to Gerbracht; No. 3,302,323 issued Feb. 7, 1967 to J. Popa; and No. 3,613,309 issued Oct. 19, 1971 to Coburn.
These various approaches to the prior art, however, fail to overcome the aforementioned problems.